The present invention relates to a device for adjusting the central position of the pistons and the angular position of the pinion in a valve driving actuator.
As is known, prior pinion-piston-rack actuators conventionally comprise a pair of pistons, rigid with related racks, and sliding in a tubular body in a meshing relationship with a central pinion, which can be turned correspondingly to a fraction of 360xc2x0, usually through 90xc2x0.
The pinion is provided for angularly driving the axis or shaft of a valve or the like and, accordingly, it must have a limited angular stroke.
In order to provide said limiting feature, it is possible to directly operate on the pinion or, possibly, on the piston-rack assembly.
In prior solutions, the above mentioned limiting effect is usually provided by limiting the outwardly displacement of the pistons.
In this connection it should be pointed out that great problems would be encountered in stopping the pistons, and consequently the pinion, during an inwardly displacement of said pistons.
The aim of the present invention is to overcome the above mentioned problems, by providing a device for adjusting the central position of the pistons in valve controlling actuators, which allows to limit the displacement of the piston toward the central pinion, in a very simple and efficient manner.
Within the scope of the above mentioned aim, a main object of the present invention is to provide such a device which can be easily controlled or adjusted from the outside of the actuator body, without requiring any difficult adjusting operations and the use of specifically designed tools.
Another object of the present invention is to provide such a device for adjusting the central position of the pistons in valve controlling actuators which, owing to its specifically designed construction, is very reliable and safe in operation.
Yet another object of the present invention is to provide such a device for adjusting the central position of pistons in valve controlling actuators which can be easily made starting from easily available elements and materials and which, moreover, is very competitive from a mere economic standpoint.
According to one aspect of the present invention, the above mentioned aim and objects, as well as yet other objects, which will become more apparent hereinafter, are achieved by a device for adjusting a central position of pistons and, accordingly, an angular position of a pinion in valve controlling actuators, comprising a tubular body, in which a first and second pistons are tightly slidably arranged, said first and second pistons being provided with opposite racks meshing with a central pinion, said central pinion being adapted to turn through discrete angles, characterized in that said device further comprises limiting means for limiting the displacement of a said piston toward said pinion, said limiting means being accessible from the outside of said tubular body.